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活动扳手常规淬火后,在缺口及圆孔处常出现表面裂纹,分析原因是由于弧裂引起的。具有弧裂形成的几何敏感部位,在淬火冷却过程中的主要功能,是显著降低那里的淬火实际冷却速度,产生缓冷效应,使局部未淬硬,产生淬火屈氏体组织,并处在马氏体的包围之中,即屈氏体软斑。并由此产生了起源于马氏体—屈氏体的不同比容和不同收缩倾向而作用于该处表面局部合成拉应力。零件在低温期内的冷速愈高,表面合成局部拉应力值越大。当其值超过材料的断裂强度时,便在那里致裂,产生沿弧面形成并扩展的弧裂。
Conventional quenching wrench after the surface cracks and holes often appear cracks, the analysis is due to arc cracking caused. The main function of the geometrically sensitive part with arc crack formation in quenching and cooling process is to significantly reduce the actual cooling rate of quenching there and produce a slow cooling effect so as not to harden locally and produce a quenched troostite structure, Surrounded by the body, that is, turtle body soft spots. And the resulting locally derived martensitic - troostite different specific volume and different shrinkage tendency to act on the surface of the local synthesis of tensile stress. The higher the cooling rate of the part during the low temperature period, the greater the local tensile stress of the surface composite. When its value exceeds the breaking strength of the material, it cracks there, resulting in arching along the camber and expansion.